1. Field of the Invention
This invention relates to a process including a shaft or deep boring in the earth, commonly known as wells, for the extraction of fluids from the earth. More particularly, this invention relates to a process for recovering hydrocarbons from a subterranean formation using a well or wells for injection and production and including heating steps.
2. Description of the Prior Art
In many areas of the world, there are large deposits of viscous petroleum. Examples of viscous petroleum deposits include the Athabasca and Peace River regions in Canada, the Jobo region in Venezuela and the Edna and Sisquoc regions in California. These deposits are generally called tar sand deposits due to the high viscosity of the hydrocarbons which they contain. These tar sands may extend for many miles and may occur in varying thickness of up to more than 300 feet. Although tar sands may lie on or near the earth's surface, generally they are located under an overburden which ranges in thickness from a few feet to several thousand feet. The tar sands located at these depths constitute one of the world's largest presently known petroleum deposits.
The tar sands contain a viscous hydrocarbon material, which is generally referred to as bitumen, in an amount which ranges from about 5 to about 20 percent by weight. This bitumen is usually immobile at typical reservoir temperatures. For example, at reservoir temperatures of about 48.degree. F, bitumen is immobile, having a viscosity frequently exceeding several thousand poises. At higher temperatures, such as temperatures exceeding 200.degree. F, the bitumen becomes mobile with a viscosity of less than 345 centipoises.
In situ heating is among the most promising methods for recovering bitumen from tar sands because there is no need to move the deposit and because thermal energy can substantially reduce the viscosity of bitumen. The thermal energy may be introduced into the tar sands in a variety of forms. For example, hot water, in situ combustion, and steam have been suggested to heat tar sands. Although each of these thermal energy agents may be used under certain conditions, steam is generally the most economical and efficient.
Thermal stimulation processes are among the most promising of the in situ methods for heating tar sand formations. In one process, commonly referred to as the "huff and puff" process, steam is injected through a well and into a viscous hydrocarbon deposit for a period of time. The well is then shut in to permit the steam to heat the oil. Subsequently, the well is placed on production.
To accelerate the input of heated fluids into the formations, it has been proposed to drill horizontally deviated wells or to drill lateral holes outwardly from a main borehole or tunnel. Examples of various thermal systems using horizontal wells are described in U.S. Pat. Nos. 1,634,236, Ranney; 1,816,260, Lee; 2,365,591, Ranney; 3,024,013, Rogers et al.; 3,338,306, Cook; 3,960,213, Striegler et al.; 3,986,557, Striegler et al.; Canadian Pat. No. 481,151, Ranney; and German Pat. No. 1,163,750, Heuckeroth. However, injection of heated fluids into tar sand formation through horizontal wells has not been developed commercially. One difficulty with these prior art methods is that hydrocarbons do not flow into the horizontal well in economic quantities.
There is a substantially unfilled need for an improved thermal method for effectively recovering viscous hydrocarbons from subterranean formation.